1. Field of the Invention
This invention relates to a Karman vortex flow meter which detects the frequency of Karman vortexes formed downstream of a prismatic member inserted in a stream of fluid, to measure the flow rate of the fluid.
2. Prior Art
A method in which the attenuation of an ultrasonic wave emitted in a fluid is measured with a signal transmitting sensor and a signal receiving sensor has been employed to detect the vortex pressure variation of a Karman vortex flow meter of this type.
However, the method is disadvantageous in the following points: The method is not economical because it uses the two sensors which are expensive. Furthermore, in the method, the extremely small sound pressure variation of the ultrasonic wave is detected in an analog mode, and therefore the detection is liable to be affected by noise. In order to eliminate the difficulty, the circuit is unavoidably intricate in arrangement.